A widely employed industrial identification or marking technology involves the formation of characters or symbols in dot matrix fashion using discrete jets of marker fluid or ink. Conventionally, this marker ink is expressed from select ones of a linear array of nozzles in conjunction with nebulizing air to form dots at the workpiece to be marked. Such fluid expression usually is controlled by a valve needle or stem which opens from a spring biased closed position under the drive of an energized solenoid. This drive pulls the stem point or terminus an adjusted distance from a valve seat. The distance between the valve pin or stem terminus or tip and the valve seat with which it cooperates typically has been in the range of 0.002 to 0.045 inch. Because of the inductive nature of solenoid drives, this opening movement of the valve pin develops at slower rates pending current build-up in the excitation coil of the drive device. Conversely, upon turning off current to the solenoid device excitation winding, it is desirable to control the resultant inductive "spike" typically encountered. Unfortunately, such control makes it more difficult to deactivate the winding for closing purposes resulting in slower or more inefficient valve operation. Thus adjustments for dot size generally have been restricted to procedures wherein control is exerted over the extent of needle travel. Such a limited form of control has resulted in constraints over the size range of dots available to the user, smaller diameter dot imprints being difficult to achieve. Further, past performance of the solenoid actuated valves used with these devices has imposed constraints on the throughput rate or line speeds acceptable for marking device requirements.
In general, the valve stem travel is determined by the distance between the rearwardly facing surface of an armature attached with the stem and a pole piece resident within the solenoid structure. Adjustment in the field is somewhat burdensome. In this regard, the devices are taken off line and mechanical adjustments are made in combination with test procedures, whereupon the assembly is remounted at the production line.
The extent of maintenance required for the marking devices at hand depends, in part, on the environment of their use, which varies from somewhat benign to quite harsh. For instance, some applications call for the marking of nascent metal components having surface temperatures of about 1800.degree. F. Typically, highly alkaline inks formed with ceramic particle suspensions are employed for such hot environments. The sticking of valve needles or stems has been somewhat common with such hot environment systems. The environments within which the markers are employed also pose difficulties to the designer in terms of the structuring and containment of their electrical control and drive systems. In this regard, it is necessary that spark potential be eliminated which, in turn, calls for the control and minimization of terminals and the like as well as a highly reliable form of power supply and control packaging.